In mobile communications networks, such as 3GPP networks (3GPP: Third Generation Partnership Project), there is a continuing need for higher data throughput. In order to achieve higher throughputs, various techniques are employed. One approach is to extensively use the limited frequency resources to obtain wide frequency bands for radio communication. This can result in a situation where two or more access nodes communicate over radio interfaces with UEs (UE: user equipment) using at least partially overlapping frequency bands.
If the two or more access nodes use at least partially overlapping frequency bands, spectral interference is likely to occur. Spectral interference can describe a situation where the radio interface between a UE and a first access node is disturbed by a radio interface of a second access node emitting power in the same frequency bands.
Spectral interference can have different effects. One possible effect is a degraded reliability of the radio interface, i.e., a higher probability for lost data packets or radio frames. This may effect the experienced communication quality in an undesired manner: voice communication may be disturbed and data communication may be delayed. In certain scenarios, even the connection between the UE and the respective access node may be lost.
A situation of spectral interference can, in particular, occur for so-called Heterogeneous Networks (HetNets). In HetNets, an access node with comparably large coverage, also referred to as macro access node, is supplemented by one or more access nodes of lower power which hence have a smaller coverage (cell size). Latter low-power access nodes are sometimes referred to as pico access nodes and can be deployed closer to the end users, e.g., on street level. Pico access nodes may be situated, preferably, in areas encountering large amounts of data traffic where there is a large demand for capacity. The pico access nodes can then reduce the load imposed on the macro access node and thereby help to increase overall throughput. Often, pico and macro nodes have at least partially overlapping cells.
In HetNets, a situation where the pico access nodes share the same frequency bands with the macro access nodes often occurs. In particular, a so-called frequency reuse of 1 is often employed where, both, macro and pico access nodes share the entire spectrum to maximize throughput. In other words: different signals may be transmitted via the same frequency band. Due to the overlapping cells, a situation of increased spectral interference may occur.
To reduce spectral interference in HetNets, inter-cell interference coordination (ICIC) can be employed. The different participating access nodes can negotiate static rules which define their share of the transmission resources in time domain and/or frequency domain. The different access nodes are therefore synchronized with each other in coordinated transmission schemes. When data traffic occurs, this data traffic is distributed into the allocated resources and thereby protected against spectral interference. For example, an access node may schedule transmission over the radio interface with a UE to a certain time-slot and/or frequency band where low spectral interference is expected based on the previously negotiated ICIC rules. For examples, the negotiated ICIC rules define a certain pattern where every n-th transmission frame of the radio interface encounters low spectral interference.
In this context, the concept of almost blank subframes (ABS) is known for the 3GPP Long Term Evolution (LTE) standard: such subframes (radio frames of the radio interface in the LTE standard) comprise a very limited amount, i.e., less than possible, of data to reduce usage of the frequency band. In ABS, for example only Cell Specific Reference Symbols (CRS) and possibly some control channel (CCH) data are transmitted in an ABS; in effect, the respective access node can be considered turned off or muted during the ABS.
However, such solutions based on ICIC encounter some limitations. For example, the overall throughput of the mobile communications network may be considerably reduced due to restrictions imposed by the shared transmission resources. Furthermore, the flexibility of protection is limited as such negotiated rules are comparably static.
Therefore, a need exists to provide efficient techniques for providing increased transmission reliability by decreasing spectral interference. In particular, a need exists for providing efficient techniques to protect transmissions against spectral interference.